Abstract: A flush valve construction for water closets, urinals, showers and the like including a cylindrical jacket and associated piston assembly. A stop is adapted to be seated in the fluid supply line which will achieve flow adjustment and also render the valve inoperative and thereby permit repairs to the construction. The shaft supporting this stop is threaded and a nut is mounted thereon. This nut is positioned for engagement with the end of the valve piston to thereby control the stroke of the piston. This enables the saving of water by preventing an undue volume of water from passing through the valve during each operating cycle.